1. Field of the Invention
The present invention relates to a laser oscillator which emits laser beam by included emission of excimer.
2. Description of the Related Art
A semiconductor laser has merits in which a laser oscillator can be drastically miniaturized and weight of the laser oscillator can be lightened as compared with the other gas lasers or solid lasers. Therefore, the semiconductor laser has been put to practical use in various fields as an optical source for sending and receiving signals by means of an optical interconnection in a photonic integrated circuit, an optical source for optical communication using an optical fiber as an optical waveguide, and an optical source used in recording on a recording medium such as optical discs, and optical memories. Further, the oscillation wavelength of the semiconductor laser extends in the range of from blue color wavelength to infrared wavelength. The semiconductor laser generally put into practical use usually includes the oscillation wavelength existing in the infrared region. Examples for the semiconductor laser in practical used include: a GaAs laser (with a wavelength of 0.84 μm); an InAs laser (with a wavelength of 3.11 μm); an InSb laser (with a wavelength of 5.2 μm); a GaAlAs laser (with a wavelength of from 0.72 μm to 0.9 μm); and an InGaAsP (with a wavelength of from 1.0 μm to 1.7 μm).
A directional characteristic or a diffraction limit in narrowing beam spot of laser beam down by an optical system depends on the wavelength of laser beam. More specifically, it is known that the shorter the wavelength is made, the more the directional characteristic is increased, which further reduces the diffraction limit. When the directional characteristic of laser beam is enhanced, disclination can be suppressed, and therefore the accuracy of sending and receiving signals via the optical interconnection in the optical communication and the photonic integrated circuit can be enhanced. As result, higher integration of the photonic integrated circuit can be achieved. In addition, when the diffraction limit is reduced, the beam spot of laser beam can be further narrowed down, and high-density recording in a recording medium such as the optical disk, and the optical memory can be performed, thereby realizing a high-capacity recording medium. As result, the formation of laser beam having shorter wavelength is a significant problem in any field using the above-mentioned semiconductor laser. Researches related to practical application of the semiconductor laser having an oscillation wavelength in the visible region have been activated.
An organic semiconductor laser having 510 nm of peak wavelength λ is disclosed in the following patent document.
[Laid-Open Disclosure Public Patent Bulletin 1]
JP 2000-156536 (page 11)
As a method for exciting (pumping) the semiconductor laser, a method of forming junction and injecting carries, an electron-beam excitation, an optical excitation, an excitation method of using avalanche breakdown and the like are known. In order to obtain included emission from the semiconductor laser, it is necessary to impart strong energy (pumping energy), which can generate a population inversion, to a semiconductor functioning as a laser medium by using the aforementioned excitation methods. However, the formation of the state in population inversion is inadequate to oscillate laser beam in practical, and therefore pumping energy higher than a threshold level, which is necessary for initiation of oscillation, must be imparted to the laser medium.
Since the level of pumping energy required for the initiation of oscillation is dependent upon the characteristics of substances that constitute the laser medium, the level varies according to the kind of the semiconductor laser. Preferably, in case of using the semiconductor laser having lower pumping energy for oscillation, a conversion efficiency to photon output from excitation input is higher, and, hence, power consumption can be suppressed. Therefore, the semiconductor laser, which can enhance the conversion efficiency of photon output while suppressing pumping energy, is anticipated. In particular, in the field in which low power consumption is directly linked to the commercial value, the improvement of the conversion efficiency of the semiconductor laser is highly expected.